All-season tires used year-round must be capable of handling various types of road surface conditions, such as dry, wet, and snowy. A tire comprising, for example, two outer circumferential main grooves disposed to the outside in a tire width direction and a shoulder land portion formed in regions to the outside of the outer circumferential main grooves in a tire circumferential direction is known in the art as a tire possessing the ability to handle various types of road surface conditions (see Japanese Patent No. 3482033B). The tire of Japanese Patent No. 3482033B is provided with shoulder lug grooves in the regions of the shoulder land portions that extend from the outer side in the tire width direction to the outer circumferential main grooves and form a plurality of land portion blocks. Shallow-grooved regions in which the groove depth is shallow are formed in the shoulder lug grooves in the regions closer to the outer circumferential main grooves, and shoulder sipes that connect to the outer circumferential main grooves are formed in these shallow grooved regions.
In accordance with the tire of Japanese Patent No. 3482033B, the shoulder sipes in the shallow grooved regions close in response to external forces acting in the tire circumferential direction, allowing block rigidity to be maintained, and external forces acting in the tire width direction mitigate block rigidity, allowing for increased ground contact and maintaining wet steering stability.
An all-season tire preferably exhibits wear resistance on dry road surfaces, and steering stability on wet and snowy road surfaces. However, the tire disclosed in Japanese Patent No. 3482033B does not exhibit a sufficient balance between these various capabilities.